High-resolution sensing of piezo-electric transducers

ABSTRACT

In a driver for a piezo-electric transducer, when a converter circuit and a sensing circuit are the same circuit, many limitations exist on the accuracy of the sensing, due to multiple parasitic effects arising from the interconnection of the power devices. These limitations may limit viability of the sensing for many applications, in particular an accurate determination of when the force on the piezo-electric transducer is fully removed. Providing an additional switch in the sensing circuit configured to repeatedly zero the sensed voltage across the piezo-electric transducer each time the sensed voltage reaches a threshold voltage generates a plurality of voltage segments between zero and the threshold voltage. Accordingly, a controller may then be configured to generate a digital reconstruction of the sensed voltage across the piezo-electric transducer by adding the plurality of voltage segments.

TECHNICAL FIELD

The present invention relates to a driver circuit for piezo-electric or electro-active transducers, and in particular to a driver circuit with higher-resolution sensing for piezo-electric transducers.

BACKGROUND

In conventional haptic feedback systems, which use the piezo-electric effect, a driver circuit applies a high-voltage signal to the piezo-electric transducer, and in response to the applied high-voltage signal, the piezo-electric transducer generates a mechanical movement sufficient to give a haptic sensation to a user. In addition, when a force is applied to the piezo-electric transducer by the user, a sensing circuit generates a sensed voltage signal, which enables the piezo-electric transducer to act as a switch.

When the driver circuit and the sensing circuit are the same circuit, many limitations exist on the accuracy of the sensing, due to multiple parasitic effects arising from the interconnection of the power devices. These limitations may limit viability of the sensing for many applications.

An object of the present invention is to overcome the shortcomings of the prior art by providing a higher resolution sensing driver circuit for any electro-active transducer, such as a piezo-electric transducer.

SUMMARY OF THE INVENTION

Accordingly, the present invention relates to a method of operating a piezo-electric transducer with a piezo-electric driver circuit, including a first switch with a first parasitic conduction path, the method comprising:

repeatedly sensing a first sensed voltage generated by a first force applied to a first piezo-electric transducer;

discharging the first sensed voltage each time the first sensed voltage approaches a first trigger level of the first parasitic conduction path, thereby generating a plurality of first voltage segments; and

determining a first total sensed voltage across the first piezo-electric transducer from the plurality of first segment voltages.

Another aspect of the present invention relates to an apparatus for operating a first piezo-electric transducer, configured for coupling to a voltage source, which provides an input voltage, and configured to transmit a drive voltage across the first piezo-electric transducer, the apparatus comprising:

a driver circuit, comprising a first driver circuit switch including a first parasitic conduction path, configured to be connected to the first piezo-electric transducer, the driver circuit configured to receive the input voltage and transmit the drive voltage for generating a force or displacement response on the first piezo-electric transducer;

a sensing circuit configured to sense a first sensed voltage generated by a first force applied to the first piezo-electric transducer, the sensing circuit including a first sensing switch; and

a controller configured to control the first driver switch and the first sensing switch, to discharge the first sensed voltage each time the first sensed voltage approaches a first trigger level of the first parasitic conduction path generating a plurality of first segment voltages, and configured to determine a first total sensed voltage across the first piezo-electric transducer from the plurality of first segment voltages.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein:

FIG. 1 is a schematic diagram of a piezo-electric transducer system in accordance with an embodiment of the present disclosure;

FIGS. 2A and 2 b are schematic diagrams of a piezo-electric transducer driver circuits in accordance with an embodiment of the present disclosure;

FIG. 3 is a schematic diagram of a piezo-electric transducer system in accordance with an embodiment of the present invention;

FIG. 4 is a plot of output voltage vs time for the piezo-electric transducer system of FIG. 3 without executing the sense/drive algorithm;

FIG. 5 is a plot of output voltage vs time for the piezo-electric transducer system of FIG. 1 or 3 while operating the sense/drive algorithm;

FIG. 6 is a flow chart of an algorithm for controlling a piezo-electric transducer;

FIG. 7 is a schematic diagram of a multi-channel piezo-electric transducer system in accordance with another embodiment of the present disclosure;

FIG. 8 is a plot of voltage vs time for a piezo-electric sensing voltage for a conventional multi-channel piezo-electric transducer system; and

FIG. 9 is a plot of voltage vs time for a piezo-electric sensing voltage for the multi-channel piezo-electric transducer system of FIG. 7.

DETAILED DESCRIPTION

While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art.

FIG. 1 illustrates a piezo-electric transducer system 1 that may use a piezo-electric transducer P₁ or some other form of transducers, such as electro-active polymer transducers, both as an actuator for driving, e.g. haptic feedback, and for force sensing, e.g. a switch or level control. Typically, circuits are designed to either drive the piezo-electric transducer P₁ or sense a force applied to the piezo-electric transducer P₁. When combining both functionalities in the same system and/or when operating a plurality of piezo-electric transducers simultaneously, complications arise from the parasitic paths created by the output devices (transistors) of the driver section of the system. Conventional systems, such as those disclosed in EP 3065029 (Kyocera), require four or five switches in addition to the drive and detection units to change between the different modes and isolate the parasitic paths.

The piezo-electric transducer system 1, includes a piezo-electric transducer circuit 2 comprising an input stage 3, a driver stage 4, an amplifier bias/switch control 5, and an output stage 6, including a piezo-electric transducer P₁ or some other electro-active transducer. The piezo-electric transducer circuit 2 may be implemented in a single chip or using discrete parts due to the high power to process. The input stage 3 may include or be connected to a high-voltage voltage source V_(HV), typically between 20 V and 200 V, whereby the driver stage 4 simply drives the desired driver voltage V_(DR) at a value between V_(HV) and V_(ref), which has the same magnitude as the high voltage source V_(HV) or a stepped down magnitude, e.g. typically between 20 V and 80 V, as the output voltage V_(out) at an output node 13 and to the output stage 6, e.g. across the piezo-electric transducer P₁.

Alternatively, the input stage 3 may include or be connected to a low-voltage source V_(IN), such as a battery, typically between 2 V and 10 V, preferably 3.6 V to 5V, whereby the driver stage 4 also includes a power converter circuit 18 for converting the input voltage V_(in) to a higher peak, e.g. 30V-60V, AC driver voltage V_(DR). The power converter circuit 18 may comprise a plurality of switches, e.g. power converting transistors, and other electrical components, such as inductors and capacitors for amplifying the input voltage V_(in) to the desired driver voltage V_(DR).

The driver stage 4 may include one or more driver stage switches, e.g. first and second driver transistors Q_(DR1) and Q_(DR2), configured to bias the output node 13 with the required drive voltage V_(DR) as the output voltage V_(out) for selectively transmitting the drive voltage V_(DR) to the output stage 6, The second drive transistor Q_(DR2), extending between the output node 13 and reference node 20 across the piezo-electric transducer P₁ may also be configured for discharging the output node 13, e.g. back to 0V, after the driver stage 4 actuates the piezo-electric transducer P₁ to enable normal sensing to proceed.

The amplifier bias/switch control 5 may comprise a controller 50, which controls the bias of the driver stage switches Q_(DR), e.g. the first and second switches Q_(DR1) and Q_(DR2), and if necessary the power converter switches. There are many ways to design the amplifier bias/switch control 5 to achieve a desired system specification. The controller 50 may also continuously sense the output voltage V_(out), e.g. from an output node 13, for determining whether an external force has been applied to the piezo-electric transducer P₁, e.g. by a user. In particular, the controller 50 determines whether the external force, and a resulting sensed voltage V_(Sens) from the piezo-electric transducer P₁ measured as the output voltage V_(out), exceeds an activation level, which results in the controller 50 activating the driver stage 4 to transmit the driver voltage V_(DR) to the piezo-electric transducer P₁ to generate a haptic response, e.g. vibration, translation and/or noise. The output voltage V_(out) is the voltage measured between the output node 13 and the reference voltage V_(ref), which may comprise the sensed voltage V_(Sens) and/or the driver voltage V_(DR), depending on the current activities of the piezo-electric transducer system 1. The controller 50 may also activate the driver stage 4 to transmit the driver voltage V_(DR) to the piezo-electric transducer P₁ to generate a haptic response, in response to an external instruction signal from the outside world, e.g. a host electronic device incorporating the piezo-electric transducer system 1, such as a smart watch, a smart phone or tablet.

A passive filter 8 may be provided in the output stage 6, e.g. parallel to a load 15, such as one or more piezo-electric transducers P₁, configured to filter the output, e.g. the drive voltage signal V_(DR), of the piezo-electric transducer circuit 2. The passive filter 8 is optional, but could be used without changing the high-level behavior of the system 1. The passive filter 8 may be inserted between the driver stage 4 and the load 15 to remove high-frequency content in the drive voltage signal V_(DR) before reaching the load 15. The passive filter 8 is particularly useful when the driver stage 4 uses a Class-D amplifier topology.

The reference voltage V_(ref) represents the voltage reference for the load 15, e.g. the piezo-electric transducer P₁. The reference voltage V_(ref) may be ground or any other convenient voltage in the system, e.g. V_(in).

A high voltage protection circuit 9, which may be included in the amplifier bias/switch control 5 or separate therefrom, comprises an electronic architecture that either adapts or blocks the output voltage V_(out) from the output node 13, i.e. the sensed voltage signal V_(Sens) from the load 15 and/or the driver voltage V_(DR) from the driver stage 4, to an appropriate, e.g. safe, voltage level for one or more analog to digital converters ADC 17. The one or more ADC 17 convert the output voltage V_(out), i.e. the sensed voltage signal V_(Sens) and/or the drive voltage signal V_(DR), to a digital representation, and conveys the corresponding digital value of the magnitude of the sensed voltage signal V_(Sens) and/or the drive voltage signal V_(DR) to the controller 50 in the amplifier bias/switch control 5.

A sense/drive algorithm 10, which may be in the form of computer hardware or computer software stored on non-transitory memory, either as part of the piezo-electric transducer system 1 or in a separate memory storage device, enables the amplifier bias/switch control 5, and in particular the controller 50, to accurately sense the load, e.g. the sensed voltage V_(Sens) across the piezo-electric transducer P₁, even when the sensed voltage signal V_(Sens) would trigger a parasitic conduction path, e.g. forward bias a body diode, of any of the driver transistors Q_(DR) directly connected to the piezo-electric transducer P₁, e.g. the first or the second switches Q_(DR1) and Q_(DR2), during various applications. For example: during removal of a force on the piezo-electric transducer P₁ after actuation of piezo-electric transducer P₁, a negative voltage, e.g. −2 V, may be generated, which causes parasitic leakage in at least one of the driver transistors Q_(DR), e.g. the second switch Q_(DR2), and prevents the controller 50 from accurately determining the force that has been applied to the piezo-electric transducer P₁, in particular if the force and resulting sensed voltage V_(Sens) is large enough to exceed the activation level.

Accordingly, a sensing switch Q_(S) may be provided to repeatedly zero the output voltage V_(out), i.e. the sensing voltage V_(Sens), from the output node 13 to enable a compilation of voltage segments used to determine the actual sensing voltage V_(Sens). For example, the sensing switch, e.g. a sensing transistor Q_(S), may be connected between the piezo-electric transducer P₁, e.g. the output node 13, and the reference voltage, e.g. V_(ref), V_(in) or ground, with a control terminal, e.g. a gate, connected to the controller 50, which enables the sensed voltage V_(Sens) across the piezo-electric transducer P₁ to be zeroed, i.e. discharged, to the reference voltage V_(ref), when needed, as hereinafter disclosed in detail. The second driver switch Q_(DR) or some other suitable switch, e.g. transistor, already provided in the piezo-electric transducer system 1 may also be used as the sensing switch Q_(S).

A communication interface 19 enables the system 1 to receive and send signals relating to driving the one or more piezo-electric transducers P₁ and/or sensing a force application on the one or more piezo-electric transducers P₁ to and from the outside world, e.g. the host electronic device incorporating the piezo-electric transducer system 1, such as a smart watch, a smart phone or tablet. Activation of the piezo-electric transducer P₁ may provide an indication to the host device of any form of user input, e.g. on/off, volume up, volume down, enter, etc.

FIGS. 2A and 2B represent two embodiments for piezo-electric transducer circuits 2. The driver stage 4 may be based on different amplifier architectures, e.g. Class-A, Class AB, Class D, etc, but from an architecture and component perspective, the load 15, e.g. the one or more electro-active or piezo-electric transducers P₁, is connected between the output node 13 and the reference voltage node V_(ref) or node 20 for a unipolar output (FIG. 2A). For a bipolar output, e.g. FIG. 2B, each end of the load 15 is connected at a different output node 13+ and 13−. In all cases, the output voltage V_(out) at the output nodes 13+ and 13−, e.g. the driver voltage V_(DR) and/or the sensed voltage V_(Sens), may be controlled minimally by one or more switches, e.g. transistors Q_(DR1+), Q_(DR1−), Q_(DR2+), and Q_(DR2−), enabling the current to flow between the high voltage supply V_(HV) or V_(in) (or current source) and the reference voltage V_(ref), e.g. reference node 20 across the load 15.

One exception is presented in FIG. 3, which illustrates a two-transistor architecture as described in U.S. Pat. No. 10,199,555, issued Feb. 5, 2019 in the name of Simon Chaput, incorporated herein by reference. The two-transistor driver stage 4 enables the sinking and sourcing of current in the load 15 through the second switch Q₂. In all figures, the body diode of the first and second switches Q₁ and Q₂ are represented by a diode symbol to show explicitly the parasitic path. For all transistors, if a conducting terminal to conducting terminal, e.g. Drain-Source (VDs), voltage becomes negative enough, e.g. above the leakage or turn-on voltage of the body diode of the second switch Q₂ connected to the load 15, the current will start to flow from the first conducting terminal, e.g. source, to the second conducting terminal, e.g. drain, via the body diode. The leakage voltage at which the current will start to flow in the diode may be between 0.2 V and 0.7 V typically depending on the exact device and semiconductor technology used. To ease the explanation, we are assuming an N-type MOS transistor is used; however, a skilled person in the art will recognize that a similar situation happens with other transistors, e.g. P-type devices.

The piezo-electric transducer system 1, includes the piezo-electric transducer circuit 2 comprising the input stage 3, the driver stage 4, the amplifier bias/switch control 5, and the output stage 6. The piezo-electric transducer system 1 may be implemented in a single chip or using discrete parts due to the high power to process. The input stage 3 may be connected to the voltage source V_(IN), such as a battery, typically with an input voltage V_(in) of between 6 V and 20 V, preferably 9V to 16V. The driver stage 4 may be comprised of the power converter circuit 18 including a forward-boost/reverse-buck converter that generates a clean sine waveform. The power converter circuit 18 of the driver stage 4 may include an inductor L₁ connected to the voltage source V_(IN), and the driver stage switches, e.g. driver transistors Q_(DR), consisting of a first low side switch Q₁ connected between the inductor L₁ and ground, and a second driver switch Q₂ connected between the inductor L₁ and the output stage 6. The control terminal, e.g. gate, of the transistor in the first switch Q₁ may be connected to a first gate driver 11 in the amplifier bias/switch control 5, and the control terminal, e.g. gate, of the transistor in the second switch Q₂ may be connected to a second gate driver 12 in the amplifier bias/switch control 5. Both the first gate driver 11 and the second gate driver 12 may be connected to the controller 50, which sends control signals to the first and second gate drivers 11 and 12 to control operation of the first and second switches Q₁ and Q₂, respectively.

While the aforementioned embodiment is described being used for sine waveforms, persons having ordinary skill in the art will appreciate the embodiments described herein may operate upon arbitrary and complex analogue waveforms, for example, square, triangular, AM modulated, FM modulated, and are not limited to operating upon sine waveforms.

The input stage 3 may include a filter capacitor (C_(VIN)) connected across the low voltage source V_(IN) and ground, and a sense resistor (R_(S)) connected between the low voltage source V_(IN) and the single inductor L₁. The single inductor L₁ may be connected between the sense resistor R_(S) and a switching node SW of the driver stage 4. A current sensor 7, which may be included in the amplifier bias/switch control 5, may be connected on either side of the sense resistor R_(S) and to the controller 50 for measuring the current, and/or the voltage entering the inductor L₁ and the driver stage 4. The current sensor 7 provides bidirectional current sensing in all possible switching condition during operation, for example, borderline conduction mode, discontinuous conduction mode and continuous conduction mode. The current feedback sensor 7 ensures the first switch Q₁ and the second switch Q₂ turn on/off at the right time to avoid high switching losses at the switching node SW.

The second switch Q₂ may be an N-type transistor including a first conducting terminal, e.g. source, connected to the switching node SW and referenced to the switching node voltage V_(sw), a second conducting terminal, e.g. drain, connected to the load 15, and a third control terminal, e.g. gate, connected to the controller 50. In order to control the control terminal appropriately, a level shift block 14, which may be included in the amplifier bias/switch control 5, translates a control signal from the controller 50 referenced to ground into a signal referenced to a switching node voltage V_(sw) at the floating switching node SW. Under the first embodiment the level shift block 14 enables scaling of a digital control signal amplitude from a digital logic level to a higher amplitude suitable for the second switch Q₂, for example, scaling from 1.8V to 5V.

The level shift block 14 may change the reference voltage V_(ref), i.e. the reference node 20, for the drive voltage signal V_(DR) from ground to an arbitrary floating node, in this case, the switching node SW. While FIG. 3 illustrates an N-type transistor for the first and second switches Q₁ and Q₂, in an alternative embodiment, a different type of switch, e.g. a P-type transistor, may be used with similar requirement for a level shift block. For P-type switch transistors, the level shift block 14 may use a floating bootstrap supply (not shown) to provide the desired level for the output of the level shift block 14.

Although desirable that the differential drive voltage signal (V_(DR)−V_(IN)) be very clean, it is not necessary for the output voltage V_(out), e.g. the drive voltage signal V_(DR) or the sense voltage V_(Sens) at the output node 13 to be referenced to ground. The high voltage protection circuit 9 may include a difference amplifier 16, which measures continuously the differential drive voltage between the reference voltage V_(IN) and the output voltage V_(out) at output node 13, i.e. the drive voltage V_(DR) and/or the sensed voltage V_(Sens), and converts the difference to a single-ended signal fed to the analog-to-digital converter (ADC) 17, which provides a digital representation of the output voltage V_(out), i.e. the drive voltage signal V_(DR) and/or the sensed voltage V_(Sens) to the controller 50.

The communication interface 19 may comprise a serial peripheral interface (SPI), which implements a communication protocol that enables an external microcontroller (or other device, for example, a computer) to send/receive information to/from the piezo-electric transducer circuit 2 via the controller 50, such as a reference waveform and internal settings used for the particular implementation. It should be noted SPI is an example of one of several digital communication protocols that may be implemented to interface with the controller 50. Other examples of a communication interface include, but are not limited to I2C, TDM, and I2S.

The inductor L₁, may be a 10 μH inductor. The inductor L₁ value may be selected in order to: (1) achieve a target distortion, e.g. lower inductance increases switching frequency and decreases distortion/THD+N, and/or (2) minimize the switching frequency, e.g. in general, a lower switching frequency corresponds to lower power consumption.

The first and second switches Q₁ and Q₂ may be of the same type, which may be the most practical choice for an integrated circuit (IC) implementation, although embodiments with mixed switches may be used. The first and second switches Q₁ and Q₂ may comprise, for example, GaN, PMOS, among other possible switches.

The output stage 6 may be referenced to the input voltage V_(in) instead of GND. The output stage 6 may include the filter 8, e.g. a capacitor C_(HV), and the load 15, for example one or more of the piezo-electric transducers P₁. Therefore, to obtain 0 V differential across P₁, the drive voltage V_(DR) and the input voltage V_(in) may be equal. Increasing the drive voltage V_(DR) across the load 15 above the input voltage V_(in) may be provided by the power converter circuit 18 of the driver stage 4.

In the piezo-electric transducer system 1 illustrated in FIG. 3, the conversion ratio, e.g. voltage amplification, of the power conversion circuit 18 may be greater than 10×, and preferably between 10× and 20× for a 50 to 120 V_(AC) drive voltage V_(DR) from a, e.g. 3.6-5 VDC input voltage V_(in). Initially, the controller 50 turns the first switch Q₁ on and the current in the inductor L₁, which is connected to reference node 20, e.g. ground, ramps up linearly. When the controller 50 turns the first switch Q₁ off, the voltage V_(SW) at the switching node SW increases the drive voltage V_(DR) to the desired output voltage V_(out) value and current flows from the inductor L₁ through the second diode Q₂ to increment the output voltage V_(out). Here, a body diode of the second switch Q₂ may turn on or the second switch Q₂ may turn on connecting the switching node SW to the load 15 and charges the load 15, e.g. the piezo P₁. When the inductor L₁ current reaches 0, the second switch Q₂ is turned off and the switching node voltage V_(SW) goes back to 0 V. The controller 50 alternates the state first switch Q1 and the second switch Q2 to control the amount of energy sent or extracted from the load 15. In the power converter circuit 18 of the driver stage 4, since the boost converter voltage gain is most of the time larger than 2, the switching node voltage V_(SW) may decrease to a little bit less than 0 V and turns on the body diode of the first switch Q₁. Thereupon, the first switch Q₁ is turned on again under zero voltage switching condition (ZVS), thus reducing the switching losses associated to the parasitic capacitance at the switching node SW.

When the second switch Q₂ turns off, the first switch Q₁ turns on in ZVS condition. Then the first switch Q₁ stays on until the inductor L₁ accumulates enough energy to charge the switch node voltage V_(SW) to the drive voltage V_(DR). When the first switch Q₁ turns off, the switch node voltage V_(SW) rings to the drive voltage V_(DR) and the second switch Q₂ is turned on under ZVS condition thus reducing switching losses.

An issue with the piezo-electric transducer system 1 is an inability to accurately sense negative voltages across the piezo-electric transducer P₁, which are limited by a leakage or turn-on voltage V_(to), e.g. −0.3V, of a parasitic conduction path, e.g. a body diode, of at least one of the drive switches Q_(DR), e.g. the second switches Q₂. When the sensed voltage V_(Sens) across the piezo-electric transducer P₁ makes V_(Sens)−V_(sw) become less than the turn-on voltage V_(to) set by the leakage of the body diode in the drive switch Q_(DR), e.g. the second switch Q₂, the output voltage V_(out) read by the controller 50 is limited approximately to that turn-on voltage V_(t0) because all other charges created by the piezo-electric transducer P₁ are replaced by the body diode conduction which limits the change in voltage.

With reference to FIG. 4, an initial application of a force on the piezo P₁ results in the generation of a gradually increasing, e.g. positive, sensed voltage V_(Sens) across the piezo P₁ and the output voltage V_(out) read by the controller 50 following the sensed voltage V_(Sens), i.e. increasing from zero to a maximum voltage, e.g. 2.0 V. When the sensed voltage V_(Sens) reaches the activation level, e.g. 1.8 V, a drive voltage V_(DR) is forced on the piezo-electric transducer P₁ to generate a haptic feedback event increasing the output voltage V_(out) by the drive voltage V_(DR), e.g. to over 50 V. The haptic event terminates by setting the voltage across P₁ to 0 V. However, releasing the force or pressure on the piezo P₁ now generates a gradually decreasing sensed voltage V_(Sens) and output voltage V_(out), which may become a negative voltage less than the turn on voltage V_(to), e.g. −0.3 V, of the body diode of one of the drive switches Q_(DR), e.g. the second switch Q₂. Unfortunately, at lower voltages, i.e. larger negative voltages, the sensed voltage V_(Sens) across the piezo P₁ becomes less than an upper limit set by the leakage or turn on voltage V_(to) of the body diode in the second switch Q₂, and the output voltage V_(out) read by the controller 50 is limited to that upper limit voltage because all other charges created by the piezo P₁ are replaced by the body diode conduction which limits the change in measured output voltage V_(out).

FIG. 5 illustrates a typical use case for a haptic system relative to the base architecture with the addition of the sensing switch, e.g. sensing transistor, Q_(S), which may be in the form of an existing driver stage switch, e.g. Q_(DR2) (FIG. 1), an added sensing switch Q_(S) (FIG. 1), or a third switch, e.g. transistor, Q₃ (FIG. 3) to enable the sense/drive algorithm 10 to be executed by the controller 50. The sensed voltage signal V_(Sens), across the load 15, e.g. piezo-electric transducer P₁, increases normally in the positive direction when a user applies a force on the piezo-electric transducer P₁ until the sensed voltage V_(Sens) reaches the activation level set to launch a haptic effect. When the activation level is reached, the different driver stage switches Q_(DR), e.g. the first and second switches Q₁ and Q₂, are biased by the controller 50 to generate the high-voltage drive voltage signal V_(DR) on the piezo-electric transducer P₁. The piezo-electric transducer P₁ transforms the drive voltage signal V_(DR) into a displacement or force via the piezo-electric transducer P₁ that is felt by the user. The sensed voltage signal V_(Sens) on the piezo-electric transducer P₁ is driven back to 0 at the end of the haptic effect using at least one of the driver stage switches, e.g. Q₂. Then when the user removes the force from the piezo-electric transducer P₁, the sensing voltage signal V_(Sens) across the piezo-electric transducer P₁ becomes negative. Accordingly, the sense/drive algorithm 10 may be used by the controller 50 to obtain an accurate representation, e.g. digital value, of a total sensed voltage V_(SensT), pieced together from segments of the output voltage signal V_(out), e.g. the sensed voltage V_(Sens), which are continually sensed, e.g. 1 kS/s-10 kS/s, providing a current interim digital representation at each sample, and then repeatedly discharged by the sensing switch Q_(S) providing a full segment digital representation each discharge, whenever the output voltage, i.e. the sensed voltage V_(Sens), approaches the turn on voltage of the parasitic conduction path, e.g. every 2-4 ms. While it is not depicted in FIG. 5, once the sensed voltage signal V_(Sens) or V_(SensT) reaches the activation level, e.g. less than −1.8 V, or a magnitude (absolute value) greater than the magnitude (absolute value) of the activation level value, a following haptic effect may be triggered.

The sensing switch, e.g. sensing transistor Q_(S), comprised of the third switch Q₃ may be connected between the piezo-electric transducer P₁ and the reference voltage, e.g. V_(ref), V_(in) or ground, with the control terminal, e.g. gate, connected to the controller 50, which enables the output voltage V_(out), e.g. the sensed voltage V_(Sens), across the piezo-electric transducer P₁ to be zeroed, i.e. discharged to the reference voltage, when needed. Accordingly, the third switch Q₃ may be activated by the controller 50 to zero the output voltage V_(out), e.g. the sensed voltage V_(Sens) across the piezo-electric transducer P₁, each time the output voltage V_(out) approaches a trigger level of a parasitic conductive path, e.g. the turn-on voltage, (−0.3 V) of the body diode of the second switch Q₂. As a result, each time the output voltage V_(out) based on V_(Sens) reaches a threshold voltage V_(th), e.g. −0.25 V, at some level greater than the negative turn-on voltage, (or less than a positive turn-on voltage) a full voltage segment is generated and converted into a digital value by the controller 50, added to an accumulated sensed voltage value V_(acc), and then discharged by activation of the sensing switch Q_(S). A plurality of voltage segments, e.g. having a magnitude approximately the same as the threshold voltage (0.25 V) but usually greater depending on sample rate, are sequentially generated and then discharged. The sense/drive algorithm 10 executed by the controller 50 may determine, e.g. provide a reconstruction (digital) of, the sensed voltage V_(Sens) across the piezo-electric transducer P₁ from the plurality of voltage segments and, when accuracy is essential, the interim digital representation from the current sensed voltage V_(Sens), forming a digital value representing a total accumulated sensed voltage V_(SensT). For example: the sense/drive algorithm executed by the controller 50 may add up (digitally) the different voltage segments (See FIG. 5) of the output voltage V_(out) or add up (digitally) the number of times the output voltage V_(out) moves between 0 and the threshold voltage V_(t)h, thus providing a much better sensing performance for negative voltages across the piezo-electric transducer P₁. Accordingly, the controller 50 may be able to determine when the user has fully released the piezo-electric transducer P₁ and/or set a more accurate minimum negative voltage for resetting and determining a secondary force application, e.g. greater in magnitude than the activation level, on the piezo-electric transducer P₁. While the architecture in FIG. 3 required the addition of the sensing switch Q_(S), e.g. the third switch Q₃, to be able to implement the sense/drive algorithm 10, some architectures may not need an extra component, e.g. switch, to be added to implement the method, but a change in the control algorithm utilizing an existing component, e.g. switch, may be sufficient.

With reference to FIG. 6, the controller 50 may execute the sense/drive algorithm 10 in the following manner. During normal operation, the controller 50 is executing the sensing loop including sensing step 101, preferably at a typical rate between one thousand samples per second and ten thousand samples per second (1 kS/s and 10 kS/s) for applications in Human-Machine Interfaces generating interim digital representations of the current sensed voltage V_(Sens). Before entering the sensing loop, the first piezo-electric transducer P₁ is connected to the reference voltage V_(ref) on one side, e.g. V_(in), with the driver stage switches Q_(DR) and the sensing switches Q_(S) switched off creating a high impedance node 13, and enabling the controller 50 to continuously determine the output voltage V_(out), comprised of only the sensed voltage V_(Sens) i.e. for sensing a force application on the piezo-electric transducer P₁. In step 101, the sensed voltage V_(Sens) across P₁ (V_(out)−V_(ref)) is sensed. The value of the accumulated voltage V_(acc) is initially set to 0V, and the controller 50 senses and receives an interim digital representation of the sensed voltage V_(Sens) at the aforementioned sample rate, e.g. every 0.1 to 1 ms.

In decision step 102, the controller 50 determines if the voltage across the piezo-electric transducer P₁ is approaching the trigger level of any one of the parasitic paths in the circuit, by, e.g. determining if the sensed voltage V_(Sens) is above the threshold voltage V_(th) or between the threshold voltage V_(th) and the turn-on voltage V_(to) of some or all of the parasitic paths. As shown in FIG. 5, a single parasitic path existed in the implementation of FIG. 3 when the sensed voltage V_(Sens) across the piezo P₁ was becoming negative enough. However, FIGS. 1 and 8 show cases in which an upper bound and a lower bound on the sensed voltage V_(Sens) across the piezo P₁ may trigger parasitic paths. Consequently, decision step 102 verifies if a parasitic path will be triggered by the current sensed voltage V_(Sens) across the piezo P₁. While the decision shows a single condition, in a real application, multiple conditions may be tested. If none of the conditions are true, i.e. the sensed voltage V_(Sens) across the piezo P₁ is not close to triggering a parasitic path, the algorithm 10 proceeds to totalling step 103, in which the total sensed voltage V_(SensT) is equal to the sum of the current value of the accumulated voltage V_(acc) (result of accumulation step 105 as hereinafter described or 0 V if no parasitic path previously triggered) plus the current measured sensed voltage V_(Sens) across the piezo P₁, as per the current sample, i.e. the interim digital representation. The sensing loop then proceeds to comparison step 104, where the value of the sensed voltage V_(Sens) or the total accumulated sensed voltage V_(SensT) is compared to one or more arbitrary activation level(s). Depending on the result of the comparison step 104, the algorithm 10 may continue in the sensing loop until the total accumulated sensed voltage V_(SensT) reaches the activation level or the algorithm 10 exits the sensing loop to drive the driver stage 4 and the piezo P₁, in driver step 107, as hereinafter described.

While the algorithm 10 cycles through the sensing loop, one of the conditions, i.e. trigger a parasitic path, at the decision step 102 may become true. When that happens, the algorithm 10 will proceed to accumulation step 105. The value of the accumulated voltage V_(acc) will be updated as V_(acc) to the sum of the current sensed voltage V_(Sens) (or V_(out)−V_(ref)) measured across the piezo P₁ based on the current sample (current interim digital representation), and the current value of the accumulated voltage V_(acc) based on the number of previously discharged sensed voltages V_(Sens) (digital representation of voltage segments). When the algorithm 10 enters the sensing loop, the value of the accumulated voltage V_(acc) is always 0 and its value is updated every time it goes through the accumulation step 105 so that the controller 50 may determine the total accumulated sensed voltage V_(SensT) generated by the piezo-electric transducer P₁ as depicted in FIG. 5 and FIG. 9. The accumulation Step 105 is a special case in which the total accumulated sensed voltage V_(SensT) equals the new accumulated voltage V_(acc). Then in discharge step 106, the sensing switch (e.g. Q_(DR) or Q_(S)) is used to discharge the voltage across the piezo P₁ to 0V. The sensing switch Q_(S) is turned on long enough to ensure a proper discharge with the filter that may be implemented. In comparison step 104, after each sample, when the controller 50 senses a total accumulated sensed voltage V_(SensT), which may be an accumulated voltage V_(acc)+a current sensed voltage V_(Sens), i.e. an interim digital representation thereof, greater than the activation level, i.e. a force application on the piezo P₁ of large enough magnitude, OR when an external prompt is sent from the host device at decision step 102, the controller 50 switches to driver step 107.

In driver step 107, the controller 50 may activate the drive voltage V_(DR) with the driver stage switches Q_(DR) and the sensing switches Q_(S) properly biased, to generate a haptic response in response to a force application on the piezo P₁ or some other notification. During the driving step 107 the driver stage switches Q_(DR), e.g. the first and second switches Q₁ and Q₂, and the sensing switching Q_(S), the third switch Q₃, are biased appropriately by the controller 50 to drive the first piezo-electric transducer P₁ to generate a haptic response to the user, e.g. some form of notification from the device, such as a force application on the piezo P₁ or in response to an external notification, e.g. a telephone call. With reference to repeat step 108, at the end of the haptic effect, the sense/drive algorithm 10 may repeat the driving step 107, if for example an external prompt from the host device requires another haptic response or may revert back to the sensing loop and wait for a user or device input. Prior to returning to the sensing loop at step 101 the controller 50 may execute first and/or second reset steps 109 and 110 by first turning on the sensing switches Q_(S) and or driver stage switches Q_(DR) to discharge the output voltage V_(out) across the piezo P₁, e.g. to 0V (step 109) and then by turning off the driver stage and sensing switches Q_(DR) and Q_(S) at reset step 110, to enable electrical charge generated by the piezo P₁ to accumulate (or drain) and make the voltage between the output node 13 (V_(out)) and the reference voltage V_(ref), e.g. V_(IN), change, so that the controller 50 accurately receives the output voltage V_(out) indicative of the sensed voltage signal V_(Sens) across the first piezo P₁.

To avoid parasitic leakage, the controller 50 may determine when the output voltage V_(out) is between the threshold voltage V_(th) and the turn on voltage V_(to) for each switch, e.g. transistor, connected to the piezo P₁, e.g. driver stage switches Q_(DR). For example, for negative voltages, the controller 50 may determine when the output voltage V_(out) is less than the threshold voltage V_(th). For positive voltages, the controller 50 may determine when the output voltage V_(out) is greater than the threshold voltage Vat. Alternatively, the controller 50 may determine when the magnitude (or absolute value) of the output voltage |V_(out)−V_(ref)| is greater than the magnitude (or absolute value) of the threshold voltage |V_(th)|. With reference to FIG. 3, the threshold voltage V_(th) (e.g. −0.25 V) corresponds to a voltage greater than the turn on voltage V_(to) (e.g. −0.3 V) of the second switch Q₂.

With reference to FIG. 1, the decision step 102 may be applied with the proper threshold voltage V_(th) and turn on voltages V_(to) for all the driving switch Q_(DR) or at least some of them, e.g. the driving switches (Q_(DR1), Q_(DR2), Q₂) directly connected to the piezo P₁ or the driving switch Q_(DR) with the turn on voltage V_(th) with the lowest magnitude or highest value. In more general terms, decision step 102 asks if the output voltage V_(out) value approaches a value which would trigger an existing parasitic path in the piezo-electric transducer circuit 2. The number of parasitic paths in the piezo-electric transducer circuit 2 may vary. In the embodiment of FIG. 1 there are 2 paths, e.g. Q_(DR1) and Q_(DR2), in the embodiment of FIG. 2b , there are 4 parasitic paths, e.g. Q_(DR1+), Q_(DR1−), Q_(DR2+) and Q_(DR2−), and in the embodiment of FIG. 3 there is 1 parasitic path, e.g. Q₂.

When the answer to decision step 102 is YES for at least one tested parasitic path, an accumulated voltage V_(acc) is computed by the controller 50 at accumulation step 105 as the sum of the previous accumulated voltage V_(acc(i-1)) plus the current voltage segment, i.e. (V_(out)−V_(ref))_(i), each voltage segment may approximately equal to or slightly larger than the magnitude of the threshold voltage V_(th). Each voltage segment is converted into a digital representation, which are added up by the controller 50. The total reconstructed voltage V_(SensT) in that situation may be equal to the sum of the digital representations of the voltage segments plus the digital representation of the current voltage segment, V_(Sens) or (V_(out)−V_(ref)).

Each time the sensed voltage V_(Sens) (V_(out)−V_(ref)) reaches a parasitic condition in decision step 102 and the accumulation step 105 is executed, a discharge step 106 may be executed by the controller 50, during which the controller 50 turns on at least one of the sensing switches Q_(S), e.g. the second driver switch Q_(DR2) or the third switch Q₃, and zeroes, e.g. discharges, the output voltage V_(out)−V_(ref) to 0 V therethrough. The sense/drive algorithm 10 then proceeds to repeat the decision step 102, at a repetition rate faster than the change in force on the first piezo P₁, which will typically occur over several milliseconds. Accordingly, in a digital system, the sensing loop may be repeated, a new sampled sensed voltage V_(Sens) obtained along with a new interim digital representation and a new total sensed voltage V_(SensT), every 100 μs to 1 ms to get a good sensing performance in a Human-Machine Interface.

When the answer to decision step 102 is NO for all parasitic paths or at least the one or more tested parasitic paths, e.g. with the lowest magnitude or highest value turn on voltage V_(to), the reconstructed or total accumulated sensed voltage V_(SensT) is computed by the controller 50 during a determination step 103 as the sum of the accumulated voltage V_(acc) and the current voltage segment, i.e. (V_(out)−V_(ref)) of the sensed voltage V_(Sens) The value of the total accumulated sensed voltage V_(SensT) represents the voltage that would be at output voltage V_(out) at the output node 13, if no parasitic path exist in the driver stage 4.

A specific example of the sense/drive algorithm 10 comprise a sensing loop, wherein the piezo P₁ continues to sense a force application, until decision step 104 determines whether the total accumulated sensed voltage V_(SensT) is greater than the activation level or the host device sends an external prompt, which will result in the controller 50 activating the driver stage 4, step 107, e.g. bias driver stage switches Q₁ and Q₂, to generate and transmit the driver voltage V_(DR) to the piezo P₁. At the end of the voltage waveform applied on the piezo P₁, e.g. a single cycle of a sine waveform with a frequency of 200 Hz and 50V amplitude, then the system returns to the sensing loop. One of the driver stage switches Q_(DR) or the sensing switches Q_(S) may turn on long enough to discharge the piezo P₁, e.g. to 0V, at step 109, and then the driver stage switches Q_(DR), e.g. the first and second switches Q₁ and Q₂, may be turned off to enable electrical charge generated by the piezo P₁ to accumulate, and thereby make the voltage between the output voltage V_(out) and the reference voltage V_(ref) increase and/or decrease with force applications on the piezo P₁, as step 110.

When the original force application continues, e.g. during the release of the force, or during a second consecutive force application, the controller 50 determines if the output voltage V_(out), i.e. the output voltage V_(out) minus the reference voltage V_(ref), representative of the sensed voltage V_(Sens), is approaching the parasitic leakage condition in step 102. In other words whether the output voltage V_(out) is a large enough negative voltage to overcome the leakage or turn-on voltage V_(to) of the body diode in one of the driver stage switches Q_(DR), e.g. the second switch Q₂, by determining if the output voltage V_(out) is greater than a predetermined threshold voltage V_(th) of at least one of the driver stage switches Q_(DR), e.g. the second switch Q₂, which is less than the leakage voltage V_(to). If the sensed voltage V_(Sens) and therefore the output voltage V_(out) reaches the threshold voltage V_(th), e.g. −0.5V, then (step 105) the controller 50 adds the voltage segment of the output voltage V_(out) between 0 and approximately the threshold voltage V_(th) typically, just above the threshold voltage V_(th), to an accumulated voltage V_(acc) in step 105. The sensing switch Q_(S), e.g. the third switch Q₃, is turned on (step 106) by the controller 50 for a length of time, which is long enough to discharge the first piezo P₁ to 0V. The accumulation process may be repeated (step 105) at a rate faster than the change in force on the first piezo P₁, which will typically occur over several milliseconds, e.g. every 1000 samples per second (1 kS/s) to 10000 samples per second (10 kS/s). During each sample, if the threshold voltage V_(th) is not met, then the total sensed voltage V_(SensT) may be calculated (step 103) by the controller 50 to be the accumulated voltage V_(acc) plus the current reference voltage segment value V_(Sens), i.e. V_(out) minus the reference voltage V_(ref), which may be 0 (for ground).

With reference to FIG. 7, a single driver circuit may be utilized to independently drive multiple loads 15, each comprising a plurality of piezo-electric transducers, e.g. P₁ and P₂ in the illustrated embodiment. The piezo-electric transducer system 21, includes the piezo-electric transducer circuit 2 comprising the input stage 3, the driver stage 4, which may include a power converter circuit, the amplifier bias/switch control 5, and the output stage 6. The piezo-electric transducer system 21 may be implemented in a single chip or using discrete parts due to the high power to process. The input stage 3 may be connected to a voltage source, such as a battery, typically generating an input voltage V_(in) of between 2 V and 10 V, preferably 3.6 V to 5V. The driver stage 4, as described hereinbefore may be a forward-boost/reverse-buck converter that generates a clean sine waveform, as described herein before. The converter stage 4 may include the inductor L₁ connected to the voltage source V_(IN), and the one or more driver stage switches Q_(DR), e.g. the first low side switch Q₁ connected between the inductor L₁ and ground, and the second switch Q₂ connected between the inductor L₁ and the output stage 6. The control terminal, e.g. gate, of the transistor in the first switch Q₁ may be connected to the first gate driver 11, and the control terminal, e.g. gate, of the transistor in the second switch Q₂ may be connected to the second gate driver 12. Both the first gate driver 11 and the second gate driver 12 may be connected to the controller 50, which sends control signals to the first and second gate drivers 11 and 12 to control operation of the driver or power converter switches Q_(DR), e.g. the first and second switches Q₁ and Q₂, respectively, as described hereinbefore.

The input stage 3 may include the filter capacitor (C_(HV)) connected across the low voltage source V_(IN) and the high voltage waveform V_(HV), and the sense resistor (R_(S)) connected between the low voltage source V_(IN) and the single inductor L₁. The single inductor L₁ may be connected between the sense resistor R_(S) and a switching node SW of the power converter circuit of the driver stage 4. As above, the current sensor 7 may be connected on both sides of the sense resistor R_(S) and to the controller 50 for measuring the current, and/or the voltage entering the inductor L₁ and the power converter circuit of the driver stage 4.

The one or more driver stage switches Q_(DR) may include a fourth (or first piezo-selecting) switch Q₄ connected between the second switch Q₂ and the first piezo P₁, which may be activated by the controller 50 to independently control the charging/discharging of the first piezo P₁, and a fifth (or second piezo-selecting) switch Q_(S) connected between the second switch Q₂ and the second piezo P₂, which may be activated by the controller 50 to independently control the charging/discharging of the first and second piezo-electric transducers P₁ and P₂, respectively, during haptic drive thereof. Zero power wake-up sensing mechanisms ZPS₁ and ZPS₂, as disclosed in U.S. patent application Ser. No. 16/136,347 filed Sep. 20, 2018 in the name of Boreas Technologies, Inc., which is incorporated herein by reference, may be provided to wake up the piezo-electric transducer system 21, in particular the first piezo-electric transducer P₁ or the second piezo-electric transducer P₂, based on a force applied to, and resulting voltage signals received from, the first piezo-electric transducer P₁ or the second piezo-electric transducer P₂.

The sensed voltage V_(Sens1) or V_(Sens2) generated by the first and/or second piezo-electric transducers P₁ and P₂, respectively, may often exceed the turn on voltage levels of the body diodes of the driver stage switches Q_(DR) or the sensing switches Q_(S). Because of the parasitic paths via the driver stage switches Q_(DR), e.g. the fourth switch Q₄ and the fifth switch Q_(S) and/or the sensing switches Q₃ and Q₆, a voltage difference between the two ends of each piezo-electric transducer P₁ and P₂ will develop when a change in force occurs thereon. When the output voltage V_(out1) or V_(out2) representing the sensing voltage V_(Sens1) or V_(Sens2) goes above the leakage or turn on voltage of the parasitic diodes of one or more of the driver stage switches Q_(DR) or sensing switches Q_(S), current will start to flow in the diodes of the driver stage switches Q_(DR) and/or the sensing switches Q_(S) which will limit the output voltage signal V_(out) available to the controller 50 based on the sensed voltage V_(Sens1) or V_(Sens2) from the piezo-electric transducers P₁ or P₂ to measure the change of force applied thereto. For example, anytime the output voltage (or the sensed voltage V_(Sens1) or V_(Sens2)): (V _(out1) or V _(out2))−V _(HV) >V _(to) (˜0.3V), e.g. for driver stage switches Q ₄ and Q ₅, OR (V _(out1) or V _(out2))−V _(ref) <V _(to) (˜−0.3V), e.g. for sensing switches Q ₃ and Q ₆, there may be a triggering of a parasitic path. There are numerous situation when this may happen, e.g. the driver stage 4 may be driving 0V across the second piezo-electric transducer P₂ while the first piezo-electric transducer P₁ is sensing a force application creating the first sensing voltage signal V_(Sens1) higher than 0.3V, which would trigger the parasitic path in the driver stage switch Q₄.

FIG. 8 illustrates the issue using the simple case of FIG. 7. When a change of force on the first piezo-electric transducer P1 generates a first sensed voltage VSens1 across the piezo-electric transducer P1 with an amplitude that is high enough to trigger one of the two parasitic diodes in one of the drive switches QDR, e.g. Q4 or Q5, then the first output voltage Vout1 based on the first sensing voltage VSens1 across the first piezo-electric transducer P1 saturates near the turn on voltage Vto of one of the drive switches QDR instead of being proportional to the force applied on the first piezo-electric transducer P1. In simple terms, once the parasitic diodes of one of the drive switches QDR saturates the first output voltage Vout1 based on the first sensing voltage VSens1, the first piezo-electric transducer P1 becomes insensitive to further change in force in the same direction.

For example, with reference to FIG. 8, for a conventional multi-piezo system, during an initial force application on the first piezo-electric transducer P₁, a positive sensed voltage V_(Sens1) will develop on the first piezo P₁ between OUT₁ and V_(ref). Assuming the driver stage 4 doesn't drive any signal, the sense voltage V_(Sens1) will develop normally in response to a force application, as in FIG. 5. However, if it happens that a second drive voltage signal V_(DR2) is applied on the second piezo-electric transducer P₂ at the same time, the first sensing voltage signal V_(Sens1) on the first piezo-electric transducer P₁ will saturate at various voltages based on the second drive voltage V_(DR2), e.g. at high voltage node V_(HV), on the second piezo-electric transducer P₂ because of the body diode in one or more of the drive switches Q_(DR), e.g. Q₄. Consequently, it is not possible to read a force applied accurately on the first piezo-electric transducer P₁ or the second piezo-electric transducer P₂ in this multi-channel architecture when a drive voltage, e.g. V_(DR1) or V_(DR2), is being sent to either of the first and second piezo-electric transducers P₁ and P₂ via high-voltage node V_(HV).

The sensing switches Q_(S) may comprise the third switch Q₃, which may be connected between the first piezo-electric transducer P₁ and a reference voltage V_(ref), with the control terminal, e.g. gate, connected to the controller 50, and a sixth switch Q₆, which may be connected between the second piezo-electric transducer P₂ and the reference voltage V_(ref), with the gate connected to the controller 50, provide similar functionality as the third switch Q₃ in FIG. 3, i.e. enable the controller 50 to independently control the discharge of the first piezo-electric transducer P₁ and the second piezo-electric transducer P₂ independently of each other in all situations. Accordingly, the third and sixth switches Q₃ and Q₆ may be activated by the controller 50 to zero the first or second output voltages V_(out1) or V_(out2), respectively, based on the first or second sensed voltages V_(Sens1) or V_(Sens2) across the first piezo-electric transducer P₁ or the second piezo-electric transducer P₂, respectively, each time the first or second output voltage V_(out1) or V_(out2) approaches the turn-on voltages, e.g. 0.3 V, of the body diodes of the driver stage switches Q_(DR) or sensing switches Q_(S), e.g. Q₄, Q₅, Q₃ or Q₆, i.e. each time the output voltage V_(out1) or V_(out2) reaches a threshold voltage V_(th1) or V_(th2), e.g. +/−0.25 V, which is less than the turn-on voltage V_(to) of the body diode of one or more of the drive switches Q_(DR) and/or sensing switches Q_(S), e.g. Q₄, Q₅, Q₃ or Q₆. A different first threshold voltage V_(th1) may be set for each driver stage switch, e.g. Q₄ and Q₅, and a different second threshold voltage V_(th2) for each sensing switch Q₃ and Q₆, or a single threshold voltage V_(th1) may be set for some or all of the piezo-selecting switches and for some or all of the sensing switches.

Typically, when sensing on the first piezo P₁, while another action is taking place, e.g. driving the second piezo P₂ or continued sensing on the first or second piezo P₁, a first (upper) threshold voltage V_(to1) (about 0.2V to 0.4V) is set for the driver stage switch Q₄ based on the second driver voltage V_(DR2) at node V_(HV) causing a parasitic trigger, and a second (lower) threshold voltage V_(to2) (−0.2V to −0.4V) is set for the sensing switch Q₃ based on the output voltage V_(out) based on sensing voltage V_(Sens2) causing a parasitic trigger. The same is true for the second piezo P₂, i.e. (V_(out))−V_(HV)>V_(to1) (˜0.3V), e.g. for switches Q₄ and Q₅ or (V_(out))−V_(ref)<V_(to2) (˜−0.3V), e.g. for switches Q₃ and Q₆.

The algorithm 10 executed by the controller 50 may digitally reconstruct the real accumulated sensing voltage V_(SensT1) or V_(SensT2) across the first piezo-electric transducer P₁ and/or the second piezo-electric transducer P₂ by adding up the different segments of the output voltage V_(out) moving between 0 and the appropriate threshold voltage V_(th1) or V_(th2), i.e. less than the turn-on voltage V_(to) of the body diode of the one or more of the corresponding drive switches Q_(DR) or corresponding sensing switches Q_(S), e.g. Q₄, Q₅, Q₃ or Q₆ thus providing much better sensing performance for sensing voltages V_(Sens1) and V_(Sens2) across the first and second piezo-electric transducers P₁ and P₂, which corresponds typically to a release in a touch interface or simultaneous or coincidental driving and/or sensing of the first and second piezo-electric transducers P₁ and P₂.

To enable independent accurate sensing on all channels, e.g. the first and second piezo-electric transducers P₁ and P₂, independently of drive activity on other channels zeroing or sensing switches Q₃ and Q₆ may be activated Accordingly, when a force is applied to the first piezo P₁, while a drive signal V_(DR2) is applied to the second piezo-electric transducer P₂, (See left side of FIG. 8) the third switch Q₃ is used to discharge the first piezo-electric transducer P₁ when the output voltage signal V_(out1) based on the first sensing voltage V_(Sens1) of the first piezo P₁ reaches either of the threshold voltages V_(to1) or V_(to2), e.g. +/−0.25V, near (less than) the leakage or turn on voltage V_(to1) or V_(to2), e.g. +/−0.3V, at which the body diode of the fourth switch Q₄ or the third switch Q₃, respectively, would start to pass current. The controller 50 may digitally determine the first total accumulated sensing voltage signal V_(SensT1) of the first piezo-electric transducer P₁ from the small segments between 0 V and the corresponding threshold voltages V_(th1) and V_(th2), e.g. one negative and one positive, to provide an accurate representation of the real sensing voltage signal V_(SensT1) from the first piezo-electric transducer P₁, as above with reference to FIGS. 1 and 2.

FIG. 9 presents the result of the method described in FIG. 6. When in sensing mode, the controller 50 monitors the sensed voltages V_(Sens1) and V_(Sens2), i.e. the output voltage V_(out1) and V_(out2), across the first and second piezo-electric transducers P₁ and P₂, respectively, continuously for an analogue implementation or at a rate that is faster compared to the measured signal for a digital implementation. In the case of a human-machine interface, the change in force will typically occur over several milliseconds, consequently a sample rate between 1 kS/s and 10 kS/s is sufficient to get a good representation of the sensed voltage signals V_(Sens1) and V_(Sens2).

With reference to the left side of FIG. 9, when the second piezo-electric transducer P₂ is actively driven by the controller 50, and simultaneously a force is applied to the first piezo-electric transducer P₁, whereby the sensed voltage signal V_(Sens1) on the first piezo-electric transducer P₁ approaches the turn on or leakage voltage of one of the parasitic diodes in the drive switches Q_(DR) or sensing switches Q_(S), e.g. the third switch Q₃ or the fourth switch Q₄, the third switch Q₃ is turned on to discharge the first output voltage V_(out) corresponding to the first sensing voltage V_(Sens1) of the first piezo-electric transducer P₁ to V_(ref), e.g. VDD. The length of time the third switch Q₃ is on will depend on several factors, such as the capacitance of the first piezo-electric transducer P₁, the conduction channel resistance R_(dson) of the third switch Q₃ and the presence of the filter 8. The third switch Q₃ should be on long enough to substantially discharge the first piezo-electric transducer P₁ from the threshold voltage to 0 V. The time may be between 100 uS and 1 ms for an exemplary embodiment. Just before turning the third switch Q₃ on, the first output voltage V_(out1) is measured and added as the current sensed voltage V_(Sens) to an accumulator in or connected to the controller 50 to add each reference voltage segment into the accumulator voltage V_(acc). The accumulator enables the controller 50 to keep track of the actual first and second sensing voltages V_(Sens1) and V_(Sens2) that would have appeared on the piezo-electric transducer P₁ or P₂ if no parasitic path existed in the switches, e.g. transistors, of the power converter stage.

For the same situation, i.e. while a drive voltage signal V_(DR2) is applied to the second piezo-electric transducer P₂, when the force is released from the first piezo-electric transducer P₁, the same problem arises as detailed above with reference to FIGS. 4 and 5.

Accordingly, the third switch Q₃ may be activated by the controller 50 to zero the first sensed voltage V_(Sens1) or the first output voltage V_(out1) measured across the first piezo-electric transducer P₁ each time the first output voltage V_(out1) approaches the turn-on voltages V_(to1), e.g. 0.3 V, of the body diodes of, e.g. the fourth switch Q₄ and/or the turn-on voltage V_(to2) of the third switch Q₃, i.e. each time the first output voltage V_(out1) reaches the threshold voltages V_(th1) and/or V_(th2), e.g. +/−0.25 V, less than the turn-on voltages V_(to). The algorithm 10 executed by the controller 50 may digitally reconstruct the real total sensing voltage V_(SensT1) across the first piezo-electric transducer P₁ by adding up a current sensed voltage V_(Sens), i.e. an interim digital representation thereof, and accumulated voltage V_(acc) from the different segments (See right side of FIG. 8) of the output voltage V_(out1) representing the sensed voltage V_(Sens) moving between 0 and just above the corresponding threshold voltages V_(to1) or V_(to2), i.e. less than the turn-on voltage of the body diode of the third and fourth switches Q₃ and Q₄, thus providing much better sensing performance for negative voltages across the first piezo-electric transducer P₁.

A voltage multiplexer 40 may be connected between the sensing switches Q_(S), e.g. the third and sixth switches Q₃ and Q₆, and the controller 50. The voltage multiplexer 40 may provide two functions: 1) multiplex the output voltage signals, e.g. V_(out1) and V_(out2), from different channels, e.g. the first piezo-electric transducer P₁ and the second piezo-electric transducer P₂, to an amplifier 41 optimized for a small input range, e.g. 100 uV to 100 mV/bit, that provides very accurate reading of the output voltages, e.g. V_(out1) to V_(outn), from the plurality of piezo-electric transducers, e.g. P₁ to P_(n), and enables high sensitivity; and 2) provide a high voltage input device to also protect the low voltage electronics from the high-voltage actuator signal, e.g. 50V, on the plurality of piezo-electric transducers P₁ to P_(n), when they are driven.

With reference to FIG. 10, the voltage multiplexer 40 may comprise a plurality of inputs, one from each piezo-electric transducer, e.g. P₀ to P_(n). Each input is connected to a high voltage switch Q_(0H) to Q_(nH), and a low voltage switch Q_(0L) to Q_(nL). A respective level shifter S₀ to S_(n) is connected between the gates of the high voltage switches Q_(0H) to Q_(nH) and the low voltage switches Q_(0L) to Q_(nL) and the controller 50, which activates a respective one of the high voltage switches Q_(0H) to Q_(nH) and the low voltage switches Q_(0L) to Q_(nL) when the sensing voltage of one of the piezos P₀ to P_(n) is being measured. The high voltage switches protects the low voltage circuitry from any signal that could damage them, typically any signal above a range 1.8V and 5V depending on the exact device used.

The method of limiting the voltage (positive and negative) below a threshold voltage V_(th), at which point current starts to leak in the body diodes of switches, e.g. transistors, connected to the piezo-electric transducers, e.g. the drive switches (transistors) Q_(DR) or sensing switches Q_(S), such as the third, fourth, fifth and sixth switches Q₃, Q₄, Q₅ and Q₆. Using the sensing switches, e.g. the third and sixth switch Q₃ and Q₆, enables the sensing voltages, e.g. V_(Sens1) to V_(Sensn), from multiple piezo-electric transducers to be read accurately and independently, while sharing the same power transistors for the driver function of the IC. The digital algorithm 10 in the controller 50 enables the sensing voltage signals, e.g. V_(Sens1) and V_(sens2), from the first and/or second piezos P₁ and P₂ to be digitally reconstructed accurately as if no parasitic path was existing. Based on that reconstructed signal, the piezo-electric transducer system 1 may be used to accurately use multiple piezo-electric transducers as sensors and play haptic waveforms on them.

The sensing algorithm provided in the controller 50 shows the following characteristics: 1) provides accurate sensing of an increase and decrease of pressure on the piezo-electric transducers P₁ and P₂; 2) compatible with multi-channel architecture; 3) may only require a single transistor, e.g. Q₃ or Q₆, per sensing channel; 4) enables driving a haptic response on one channel, e.g. piezo P₁, while sensing a force application on a different channel, e.g. piezo P₂; 5) ability to sense positive and negative voltages across multiple piezo transducers; 6) avoids cross-talk or coupling effect when sensing multiple transducers; 7) direct sensing of low voltage signal at the high voltage nodes enable high sensitivity; 8) configurable “reset” threshold to adapt the method to real parasitic path present in the system; and 9) may not need extra components for sensing than for driving.

The controller 50 for controlling the piezo-electric transducer circuit 2, for example, a digital controller, may be a computer. The controller 50 may contain a processor, a storage device, a memory having software stored therein that defines the abovementioned functionality, input and output (I/O) devices (or peripherals), and a local bus, or local interface allowing for communication within the controller 50. The local interface may be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The local interface may have additional elements, which are omitted for simplicity, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components.

The processor may be a hardware device for executing software, particularly that stored in the memory. The processor may be any custom made or commercially available single core or multi-core processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the present controller 50, a semiconductor based microprocessor, e.g. in the form of a microchip or chip set, a macro-processor, or generally any device for executing software instructions.

The memory may include any one or combination of volatile memory elements, e.g. random access memory (RAM, such as DRAM, SRAM, SDRAM, etc.)) and non-volatile memory elements, e.g., ROM, hard drive, tape, CDROM, etc. Moreover, the memory may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory may have a distributed architecture, where various components are situated remotely from one another, but may be accessed by the processor.

The software may define functionality performed by the controller 50, in accordance with the present invention. The software in the memory may include one or more separate programs, each of which contains an ordered listing of executable instructions for implementing logical functions of the controller 50, as described below. The memory may contain an operating system (O/S). The operating system essentially controls the execution of programs within the controller 50 and provides scheduling, input-output control, file and data management, memory management, and communication control and related services.

The I/O devices may include input devices, for example but not limited to, a keyboard, mouse, scanner, microphone, etc. Furthermore, the I/O devices may also include output devices, for example but not limited to, a printer, display, etc. Finally, the I/O devices may further include devices that communicate via both inputs and outputs, for instance but not limited to, a modulator/demodulator (modem; for accessing another device, system, or network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, or other device.

When the controller 50 is in operation, the processor may be configured to execute the software stored within the memory, to communicate data to and from the memory, and to generally control operations of the controller pursuant to the software, as explained above.

When the functionality of the controller 50 is in operation, the processor may be configured to execute the software stored within the memory, to communicate data to and from the memory, and to generally control operations of the controller pursuant to the software. The operating system may be read by the processor, perhaps buffered within the processor, and then executed.

When the controller 50 is implemented in software, it should be noted that instructions for implementing the controller 50 may be stored on any computer-readable medium for use by or in connection with any computer-related device, system, or method. Such a computer-readable medium may, in some embodiments, correspond to either or both the memory or the storage device. In the context of this document, a computer-readable medium is an electronic, magnetic, optical, or other physical device or means that may contain or store a computer program for use by or in connection with a computer-related device, system, or method. Instructions for implementing the system may be embodied in any computer-readable medium for use by or in connection with the processor or other such instruction execution system, apparatus, or device. Although the processor has been mentioned by way of example, such instruction execution system, apparatus, or device may, in some embodiments, be any computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “computer-readable medium” may be any means that can store, communicate, propagate, or transport the program for use by or in connection with the processor or other such instruction execution system, apparatus, or device.

Such a computer-readable medium may be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples, i.e. a non-exhaustive list, of the computer-readable medium would include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a random access memory (RAM) (electronic), a read-only memory (ROM) (electronic), an erasable programmable read-only memory (EPROM, EEPROM, or Flash memory) (electronic), an optical fiber (optical), and a portable compact disc read-only memory (CDROM) (optical). Note that the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.

In an alternative embodiment, where the controller 50 is implemented in hardware, the controller 50 may be implemented with any or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc.

The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. 

I claim:
 1. A method of operating a piezo-electric transducer with a piezo-electric driver circuit, including a first switch with a first parasitic conduction path, the method comprising: repeatedly sensing a first sensed voltage generated by a first force applied to a first piezo-electric transducer; discharging the first sensed voltage each time the first sensed voltage approaches a first trigger level of the first parasitic conduction path, thereby generating a plurality of first voltage segments; and determining a first total sensed voltage across the first piezo-electric transducer from the plurality of first segment voltages.
 2. The method according to claim 1, further comprising comparing the first sensed voltage to a first threshold voltage based on the first trigger level.
 3. The method according to claim 2, wherein the determining step includes: generating a digital representation of one of the plurality of first voltage segments each time the first sensed voltage reaches the first threshold voltage; updating a first accumulation sum with each digital representation each time the first sensed voltage reaches the first threshold voltage; and determining the first total sensed voltage across the first piezo-electric transducer from the first accumulation sum.
 4. The method according to claim 3, wherein the determining step further includes: generating an interim digital representation of each first sensed voltage, each time the first sensed voltage is sensed; and determining the first total sensed voltage across the first piezo-electric transducer from the first accumulation sum and the interim digital representation.
 5. The method according to claim 1, wherein the first switch in the piezo-electric driver circuit comprises a driver circuit switch including the first parasitic conduction path, wherein the method comprises transmitting a drive voltage to the first piezo-electric transducer for generating a force or displacement response on the first piezo-electric transducer.
 6. The method according to claim 5, further comprising: generating an interim digital representation of each first sensed voltage, each time the first sensed voltage is sensed; and wherein the step of transmitting the drive voltage includes transmitting the drive voltage when the first total-sensed voltage plus the interim digital representation is greater than a predetermined activation level.
 7. The method according to claim 5, wherein the piezo-electric driver circuit includes a second switch with a second parasitic conduction path; and wherein the method further comprises: comparing the first sensed voltage to a second threshold voltage based on a second trigger level of the second parasitic path; discharging the first sensed voltage each time the first sensed voltage reaches the second threshold voltage, thereby generating a plurality of second voltage segments; determining a second total sensed voltage across the first piezo-electric transducer from the plurality of second segment voltages.
 8. The method according to claim 1, wherein the piezo-electric driver circuit is also configured for selectively transmitting a drive voltage across a second piezo-electric transducer; and further comprising determining the first total sensed voltage across the first piezo-electric transducer while the driver circuit is transmitting the drive voltage across the second piezo-electric transducer.
 9. The method according to claim 1, further comprising: sensing a second sensed voltage generated by a second force applied to a second piezo-electric transducer; comparing the second sensed voltage to a second threshold voltage based on a second trigger level of a second parasitic path of the second piezo-electric transducer; discharging the second sensed voltage each time the second sensed voltage reaches the second threshold voltage, thereby generating a plurality of second voltage segments; determining a second total sensed voltage across the second piezo-electric transducer from the plurality of second voltages segments.
 10. The method according to claim 9, further comprising: discharging the first sensed voltage with a first sensing switch each time the first sensed voltage approaches a third trigger level of a third parasitic conduction path from the first sensing switch generating a plurality of first segment voltages; and discharging the second sensed voltage with a second sensing switch each time the second sensed voltage approaches a fourth trigger level of a fourth parasitic conduction path from the second sensing switch generating a plurality of second segment voltages.
 11. The method according to claim 9, further comprising determining the second total sensed voltage across the second piezo-electric transducer while the piezo-electric driver circuit is transmitting a drive voltage on the first piezo-electric transducer.
 12. An apparatus for operating a first piezo-electric transducer, configured for coupling to a voltage source, which provides an input voltage, and configured to transmit a drive voltage across the first piezo-electric transducer, the apparatus comprising: a driver circuit, comprising a first driver circuit switch including a first parasitic conduction path, configured to be connected to the first piezo-electric transducer, the driver circuit configured to receive the input voltage and transmit the drive voltage for generating a force or displacement response on the first piezo-electric transducer; a sensing circuit configured to sense a first sensed voltage generated by a first force applied to the first piezo-electric transducer, the sensing circuit including a first sensing switch; and a controller configured to control the first driver switch and the first sensing switch, to discharge the first sensed voltage each time the first sensed voltage approaches a first trigger level of the first parasitic conduction path generating a plurality of first segment voltages, and configured to determine a first total sensed voltage across the first piezo-electric transducer from the plurality of first segment voltages.
 13. The apparatus according to claim 12, wherein the controller is also configured to compare the first sensed voltage to a first threshold voltage based on the first trigger level.
 14. The apparatus according to claim 13, wherein the controller is also configured to: generate a digital representation of one of the plurality of first voltage segments each time the first sensed voltage reaches the first threshold voltage; update a first accumulation sum with each digital representation each time the first sensed voltage reaches the first threshold voltage; and determine the first total sensed voltage across the first piezo-electric transducer based the first accumulation sum.
 15. The apparatus according to claim 14, wherein the controller is also configured to: generate an interim digital representation of each first sensed voltage, each time the first sensed voltage is sensed; and determine the first total sensed voltage across the first piezo-electric transducer from the first accumulation sum and the interim digital representation.
 16. The apparatus according to claim 14, wherein the controller is also configured to: generate an interim digital representation of each first sensed voltage, each time the first sensed voltage is sensed; and transmit the drive voltage when the first total sensed voltage, comprising the first accumulation sum plus the interim digital representation, is greater than a predetermined activation level.
 17. The apparatus according to claim 12, wherein the driver circuit includes a second driver switch with a second parasitic conduction path; and wherein the controller is further configured to: compare the first sensed voltage to a second threshold voltage based on a second trigger level of the second parasitic path; discharge the first sensed voltage each time the first sensed voltage reaches the second threshold voltage, thereby generating a plurality of second voltage segments; determine a second total sensed voltage across the first piezo-electric transducer from the plurality of second segment voltages.
 18. The apparatus according to claim 12, wherein the driver circuit further comprise a second driver circuit switch with a second parasitic conduction path configured to transmit the drive voltage on a second piezo-electric transducer; wherein the sensing circuit is also configured to sense a second sensed voltage generated by a second force applied to the second piezo-electric transducer; wherein the sensing circuit includes a second sensing switch configured to discharge the second sensed voltage each time the second sensed voltage approaches a second trigger level of the second parasitic conduction path generating a plurality of second segment voltages; and wherein the controller is also configured to determine a second total sensed voltage across the second piezo-electric transducer from the plurality of second segment voltages.
 19. The apparatus according to claim 18, wherein the controller is also configured to: control the first sensing switch, to discharge the first sensed voltage each time the first sensed voltage approaches a third trigger level of a third parasitic conduction path from the first sensing switch generating the plurality of first segment voltages; and control the second sensing switch, to discharge the second sensed voltage each time the second sensed voltage approaches a fourth trigger level of a fourth parasitic conduction path from the second sensing switch generating the plurality of second segment voltages.
 20. The apparatus according to claim 19, wherein the controller is also configured to determine the first sensed voltage across the first piezo-electric transducer from the plurality of first segment voltages while the driver circuit is transmitting the drive voltage on the second piezo-electric transducer. 